The present invention relates to an automatic driving wheel change-over apparatus and, more particularly, to an apparatus for automatically effecting a change-over between a two wheel drive mode and a four wheel drive mode of a vehicle in accordance with the surface conditions of a road.
In the case of four wheel drive vehicles which have been used widely, the change-over between the two wheel drive mode and the four wheel drive mode is accomplished manually so that the driver must make a skilled judgement in accordance with the road surface condition, and the judgement and the corresponding operation are troublesome.
A vehicle has been disclosed in Japanese Patent Kokai (Laid-Open) No. 148,622/80 wherein, when a slip is detected during the operation, the drive of the vehicle is changed over automatically to the four wheel drive mode and the drive is changed back to the two wheel drive mode upon a disaperance of the detected operation condition.
In the case of ordinary automotive vehicles, for ease in driving it is desirable that a vehicle is capable of and automatic change-over between the four wheel drive mode and the two wheel drive mode while in operation. Thus, a control system is conceivable in which a vehicle is basically operated in the two wheel drive mode so that when the difference in number of revolutions between the front and rear wheels exceeds a predetermined value, it is determined that a slip is developed and the road surface is bad, thereby causing the vehicle to be operated the four wheel drive mode for a predetermined period of time. However, this system is disadvantageous in that, when the vehicle is running on a long snow-covered road, gravel road or the like, the change-over between the two wheel drive mode and the four wheel drive mode is repeatedly effected so that the clutch is thermally overloaded and the wear of the clutch increases thereby reducing the life of the clutch is reduced.